Inorganic pigments are often incorporated in various polymers as whiteners, tinting agents, or opacifiers. Pigments such as TiO2 are particularly useful for these purposes because it scatters light very efficiently. Such pigments may be present in pigment dispersions known from e.g. U.S. Pat. No. 5,886,069 disclosing TiO2 particles with discrete inorganic particles dispersed on the surface of the TiO2 particles. However, such dispersions are not always sufficiently stable and do not allow storing for a longer period of time without suffering from destabilization or gelling resulting in considerably lowered light scattering efficiency. Such dispersions may also suffer from optical crowding provided the TiO2 particles are contacted with each other too closely. As a result thereof, hiding power and tinting strength may become considerably reduced. Extenders have been added to paint formulations to space the TiO2 particles to preserve scattering efficiency. However, distribution of extenders is difficult and the hiding power is affected. It would be desirable to provide an aqueous pigment dispersion in the absence of dispersants such as surfactants. Surfactants may impart foaming problems to the dispersion which in turn may deteriorate water and chemical resistance.
WO 2004/035474 A1 discloses silanized colloidal silica particles in conjunction with an organic binder. Organic binders, however, may disturb the stability of a pigment dispersion. The process of dispersing pigment in the presence of organic binders may also require an additional energy input since higher shear forces may be necessary. Furthermore, the presence of organic binders reduces the amount of pigment dispersible which in turn reduces the resulting light scattering efficiency.
The present invention relates to a facilitated method of providing an aqueous pigment dispersion having improved stability. One further object of the invention is to provide a method of enabling longer storage and shelf life, and which provides for acceptable pigment properties such as light scattering efficiency when admixed in any formulation including paints.